1. Field of the Invention
This invention involves a system and a method for generating and displaying velocity field information, especially in the context of diagnostic ultrasonic imaging.
2. Description of the Related Art
For centuries, if not millennia, physicians have pinched, prodded, pulled, and poked their often cringing patients in order to better diagnose internal illnesses. In other words, physicians have long used palpation to find abnormalities in tissue. The reason for this is that the elasticity of tissue, that is, the way in which it expands or contracts in response to an externally or internally applied pressure, gives useful diagnostic information about the tissue. For example, when blood is pumped into tissue by the heart, the tissue contracts and expands in time with the cardiac cycle. In general, the more an area then expands, the more blood it may be receiving, or the more elastic it may be.
A plethysmograph is a device used by physicians to measure the expansion and contraction of tissue caused by blood flowing through the tissue. It is used by placing a fluid-filled cuff around a limb and then measuring the displacement or pressure change of the fluid. A significant drawback of this device, however, is that it gives information only about the general properties of a limb but no specific information about individual structures (for example, an artery or a muscular lesion) within the limb, or the relationship between an internal structure and surrounding structures. Moreover, devices such as the plethysmograph are unsuitable for use in examining the elasticity of organs such as the heart--squeezing a patient's chest hard enough to feel changes in his heart tissue or liver would probably render the whole diagnostic procedure moot.
It has been proposed that one could use ultrasonic imaging techniques in order to assess the elastic properties of tissue. For example, the following U.S. patents describe a technique for ultrasonic plethysmography:
U.S. Pat. No. 5,088,498 (Beach et al., 2 Feb. 1993); and
U.S. Pat. No. 5,183,046 (Beach et al., 18 Feb. 1992).
Furthermore, the article "A review of imaging techniques for assessing the elastic properties of tissue," Parker, Gao, Lerner, and Levinson, Dept. of Electrical Engineering, Univ. of Rochester, Rochester, N.Y. 14627, discusses various techniques for assessing tissue elasticity. These known methods are either difficult to implement in a normal clinical setting, do not allow for imaging in real time, or fail on both counts.
What is needed is a way to assess the elastic properties of tissue (including other properties relating to the local expansion and contraction of the tissue) with an easy-to-use system that is able to provided the information in real time.